Theres EVERY reason for it.
salary cap or not, you HAVE to use this approach. Its common sense. Obviously. The salary cap is not infinite:
more savings everywhere, means more spending everywhere.
if you do your homework and tind guys that, for whatever reason were underutilized , used incorrectly, or (my favoite) "hidden" or un-noticed behind a strong positional group (think simon last year).
Too often i find thes "big splash"!guys have trouble transitioning to a new team, scheme, players beside them, etc. plus, you spent 10% of your TOTAL budget for the year. It BETTER work out.
builing a solid team has been and always will be grounded in good scouting, good drafting, good teaching and development of YOUR OWN players. Its just your best, most consistent and reliable way to build a solid consistent winner. IMO, of course.