My Slides Are Comin'..
Hey CB,
Dug's slides are great. Anyhow, as to length....ahahahahaha....you might want to get a couple (one short, one long) and experiment as to what you want to do. Since your initial thought is to cover ALL the strings, then you have to get a slide at least 2" in length.
The vast majority of folks get slides that cover all the strings (so as to play a FULL chord in OPEN tuning), so you are in good company. Be careful that you don't get TOO LONG though as the extra weight (esp. if you slide off the pinky) can be unwieldy. I have a heavy slide that is 2.5" and I just couldn't maneuver the damn thing around at all.
There are a small minority (myself included), notably Mississsippi Fred McDowell, who use short slides and only need to cover a few strings at a time and therefore a SHORTER slide is preferrable. My DUGLY slides are right around 1.5" and since I play off my "flippin the bird" finger, the slide covers from above the knuckle to just below the tip of my finger which means I have NO trouble damping behind it.
As to your question, why would one want shorter?....Just a preference thing but for example, if I'm in standard tuning and slidin'....if I'm doing a minor blues vamp, then I spend most of my time on the first 3 strings as those 3 strings (E, B and G; high to low) make a partial barre minor chord. So, if I'm at the 5th fret, then that's Am area. A shorter slide makes for quicker maneuvering if one NEEDS it. For me, it's just more comfortable to play with a shorter slide.
OR.....if doing a major blues, then most of my time is on the B-G-D strings (high to low) and if I'm at the 5th fret, that's a C.
SLIDE is a fun guitar style to play and the avenues/paths you can go down with it are pretty varied. Of course, once you start slidin', you'll want to investigate lap style, and that is another can o'worms to open up. lol
Good luck CB and if you have any questions, just fire away and we'll be glad to help ya out. :rockon: