Funk- Some places will let you bet a teaser or parlay and fill in the rest of the picks later if you don't make all your selections when you place the bet. The standard time to fill in the rest is usually seven days but that may vary.
Example- you want to play a four team, seven point teaser or a four team parlay before the Sunday night game but you only like one play on Sunday night and one play on Monday night. You can still make the play but you leave two spots open and fill them in as you see other plays you like during the week or the next weekend.
It's always good to have that option if you choose to use it.
Are open teasers or parlays that great? I guess if you only like one team on a given week, it is a good thing. However, I can usually come up with a second team i like for my teasers.