When do you use the 2 cards to come chart?

[aargh57]

When deciding on your odds why do you use the 2 cards to come odds when making your decision? I realize on the flop you have 2 cards to come but you will frequently have to pay a double sized turn bet to see the next one so you aren't really getting those odds, right?

For example, say you have:
K [img]/images/graemlins/spade.gif[/img]T [img]/images/graemlins/club.gif[/img] on the button, 2 fold then EP2 limps, 1 more limps and you limp, SB completes, BB checks: 5 SB

Flop comes
3 [img]/images/graemlins/diamond.gif[/img]5 [img]/images/graemlins/heart.gif[/img]8 [img]/images/graemlins/club.gif[/img]

SB bets, 2 fold, 1 calls (7SB)

Now if you use the 2 cards to come odds you only need 7 to one to call. If you consider your overcards 1.5 outs each then you are getting proper odds it would seem with 3 total outs. However, what happens on the turn? If you don't improve and it's bet to you now you have to fold. You just payed 1 SB getting only 7 to one odds and you only got to see 1 card. Sorry if this is elementary but I end up using the one card to come odds more often than not because I don't want to be drawing when I don't have the odds to. Any help would be appreciated.