Now consider that, sans Premium time or other CB bonus, if you have a good match you're probably netting a little over 100K after ammo and repair costs. So if you subsequently want to buy BACK the AC20 it will take 3 good matches to make up that 300K difference.
This may not sound all that bad, but once you start selling whole chasis, custom loadouts, multiple items, etc... that 3 matches goes WAY up.
Assume a variant and loadout that would retail for 5mil. If you sell that chasis, you're going to grab 2.5mil for your trouble (as near as I can tell resale value in MWO is simply 50% retail).
Again, what does that mean in practical terms? To buy back that mech and configure the same loadout will take 25 matches (100k per match * 25). Let's say your matches are averaging 8 minutes, that's a little over 3 hours of game time... IF you take no breaks and all 25 of your matches are wins/good matches.
Realistically, that '3 hours of game time' is going to inflate quite a bit, and is probably more like two or three days of effort... just to get back to where you started.
In the long run then, you're much better off saving everything you buy and slowly accumulating a vast inventory of items which will give you a lot of flexibility in the future for changing things around and experimenting with different loadouts. It may take a little longer the first time around to get some new shiny toy then if you sold what you have, but it will speed things up in the long run.
Remember: Short term gain = long term pain.
EDIT
dangit, Mods this was supposed to be in Guides... I swear I was in that forum when I created this topic! Ah well, can you please move it?
Edited by SamizdatCowboy, 29 November 2012 - 09:49 AM.