I prefer not to. I enjoy working within the limited structure intended for the faction I am playing. I also find it opens up major shifts in availability of options to factions that were not intended to have them. For example, smoke for PanO and AD troops for JSA... I don't mind if my opponent wants to use them. though I generally appreciate a heads up at the start of the game.
Do you mean clicking the button in the army builder that allows for all the extra mercs? No, I like that some armies lack certain tools which makes building lists around such weaknesses more interesting. The mercs already allowed in my lists I do take from time to time. The Krakot Renegade is wonderful, Knauf's new kit with +1 burst on his sniper is cool. Libertos are cheap minelayers and Monstruckers do good work as engineers with drop bears. Not to mention the value of a CSU as a cheap specialist choice.
I tend to not use them as I'm very attached to faction identity, but I'll break one out once in a while if they're a great fluff match or offer a fun and different play experience. For example, I'd never take a Libertos outside of a strict win-at-all-costs, no fun allowed tournament, but CSUs sometimes make appearances in my NCA if I'm running a lighter, less overtly military list, and troops like Bounty Hunters or Aida get brought out if I'm feeling like some random casual fun. I used Mercs much more than usual in MRRF thanks to the strong fluff connection with the Anaconda company, the good fits with crunch, and because they opened new options without being strictly better or worse than native approaches to the same problems.
Thank you all for your answers. <<<<<>>>>> Yes that was exactly what I wanted to say (maybe I didn't explain it well)
