Lost Legion Rules, page 9 wrote:
Healing points provided by effects stack and you can use them to heal your Units or Hero anytime during your turn. Unused healing points are lost once you start a combat, or at the end of your turn.
So you may save healing points for some short durations. This is important because otherwise it would be very hard to heal high level units easily, and sometimes the timing flexibility is useful for other reasons.
Whether you play a deed card for healing or buy healing at a village/ monastery they function the same - each gets you healing points that follow the same rules.