I apologise in advance for this post as it might come a bit preachy and arrogant
Firstly, I'd point blank say that there are no "free" bets. I actually go on a rant whenever I get chance about it... not just in bookie offers, but everyday life. Companies advertise "Buy one get one free"... well that isn't FERE is it... it is just a 'good value deal'. Unless you can literally walk in to a shop and take it, without exchanging anything at all in return IT IS NOT FREE. I lose my rag with anyone that doesn't understand that concept. Now that shouldn't be confused by me saying "nothing is free", because some things are... a supermarket giving away free samples/tasters, is free. It also doesn't mean when something is advertised as "free", that I don't think it's good value... which leads me nicely on to "free bets"
They are not free (HF is right that incredibly rarely you get a "free bet with no desposit required" - which technically is free, however there is usually a play through that you need to get throiugh which makes them less valuable.
I personally do like to 'collect' free bets where I can.
In the opening post, point one mentions Skjy and their £25 stake, get a £5 free bet. Now I bet around £200-400 a weekend generally so I easily go over that without even thinking about it. I do have access to 4 slybet accounts at the moment though and I don't use any but my own for these "free bet club". Similarly, PaddyPower do 5x £10 bets and you get a £10 "free bet". I don't always use PP but lean that way if I remember to.... I still chase the best price rather than ones I know will get me a 'free bet'. However, the amount I stake a weekend doesn't make it that difficult to hit the qualifiers for those bets.
I should make it clear though, that I am profitable weekend-to-weekend, so I am not losing £25 and then £50 with Sky and PP just to get £15 worth of free bets. I see them 100% as a bonus, I never use them for anything during the weekend/week that I'm betting on, so they are never factored into my returns.
The method I do more actively 'search' for free bets is with the "money back if loses" offers. Mainly with Sky. The first ITV race is usually the offer and I'll always start my weekend punting by concentrating on that race on a Friday night (perhaps it is second after whatever the 'big race' of the weekend is) Now I don't always bet in the race... I still have to fancy the selection however if I am brutally honest, if I don't have a strong selection, I would perhaps just put the £20 on the fav and it's an on-going joke I have with a couple of my friends that we actually want it to come 2nd for the "Cheltenham bet". I haven't actually got accurate stats on the money back races, but I'd be staggered if I hadn't had more winners and "free bets" than losers, let alone actual decent price winners. I do also have the luxury of having 3 extra accounts I can use, so when I really fancy one I can increase the stake. (I am actually a bit annoyed Ista gets £50 for the same consession but imagine that is based on my staking history, as I've only really increased stakes in the past 18 months)
I find the PP ones "if horse X wins you get money back" or "if you come 2nd to blah money back" to be rubbish value. I feel like that usually is me giving £10 away to get a £10 free bet, and I always try and think "would I stake £10 on Cheltenham now instead" - and often that'd be yes. I'd need to really want to oppose a favourite to use the PP "free bet" offer and to be honest £10 isn't a big enough stake for me to have a normal bet on now, so I'd just look for the bigger price.
Every single weekend I aim to make a profit (well done Captain Obvious) - and I pick up free bets where I can to use on Cheltenham to help me with my quite specific approach of backing multiple horses / building a book / increasing returns on very strong selections / covering horses I am too scared to put my 'real money on'
For me, "free bets" are the bi-product of me successfully punting, and not my main focus. I do like the free bets because it'll effectivly and significally 'skew' the festival for me. What I have in my bank account on the Monday before Cheltenham compared to the Monday after will be affected by landing some "free bets". I am just lucky that I can cover the 'losses' that have provided the free bets during the season whilst still making a profit.