The Celtic Cross is such a long and involved spread that lots of people prefer to do three-card readings. The three-card readings can be varied in many many ways. Past, present, future or body, mind, spirit, or he needs, she needs, relationship needs-----you can think of tons of variations on the spur of the moment and then draw clarifiers for any of the positions, so I'd say it's the one that would be a general all-purpose spread, naming the positions yourself as you go along.
Really, it's not hard to make your own spreads on the spur of the moment if you just think of the facets of the situation that need answers. I usually find that 7 cards work well for me. Sometimes I read them straight along, like a story sort of. Sometimes I use cards 1 and 2 as the recent past, cards 3,4, and 5 as the present, and 6 and 7 as the near future.
Today I did a couple of quick three-card spreads, one for a "what if I do" and one for a "what if I don't", with the positions in each spread answering the question "what affect will this action I'm considering have on (card 1) myself (card 2) the kids and (card 3) the household in general."
Sometimes for relationships I do a quicker, shortened version of what we on AT have been calling Umbrae's relationship spread----I lay two cards side by side to represent him and her and then put a third card below and kind of between them so the three cards kind of form a V and that way I can read the two people side by side as well as seeing the relationship card next to each of the cards representing the people, if that makes a good mental picture the way I'm explaining it.
I think the important thing is just to have a name for each of the positions you put cards in----know for sure what facet of the question you want that card or group of cards to answer.
I found that trying to memorise a bunch of spreads was nearly impossible for me and that making my own up as I went along was the best option. I keep the spreads simple and then I draw clarifying cards for any position I feel needs some further information.