In practice, though, I found they are very difficult to align precisely and even a very shallow dado / groove or biscuits (though that's another tool) would have helped with alignment immensely.
Where a butt joint is an appropriate joint to choose the difficulty in alignment is their main downside. There are simple construction tips that can help overcome these problems, including creative use of clamps and registration surfaces (e.g. a stop block, or just the top of the workbench sometimes) to butt matching surfaces against1 but there's no denying it can be a tricky thing to do in practice.
Having the glued-up pieces slide around while trying to tighten down clamps or nail in a brad with the pneumatic nailer was frustrating, and would have been a moot point with a different kind of joint.
Yep, all wood glues are very lubricative and they can make a joint surprisingly slippery!
Anything in the same vein as a biscuit (including dowels, Dominos and splines) is one of the primary ways to fix alignment and stop things slipping around during glue-up because they lock in the positions of the two pieces of wood, sometimes relevant to the face sides only (biscuits) other times both up and down as well as side to side (dowels and Dominos).
But when making up large panels from a number of boards there's really no reason to resort to any of these because you can use a caul to force alignment as you are clamping up.
Note that splines, dowels, biscuits and Dominos don't add any needed strength in a joint like this and in fact may slightly weaken the joint as paradoxical as that seems.
Are there any other not-so-obvious drawbacks to butt joints, that may not be apparent to (beginner) woodworkers?
Other than being careful where one or both faces is end grain I don't think so. Anywhere that face grain is glued to face grain (whether longitudinal or radial) the joint created will be at least as strong as the wood around it.
This assumes the joint faces are properly prepared of course. They should be:
- Flat (or occasionally with a deliberate curve, as in a sprung joint).
- Smooth (the smoother the better, roughening the surface is almost never desirable).
- This last one doesn't get mentioned often enough — freshly worked (older wood surfaces don't glue as well as those which have just been worked, ideally within an hour).
And on top of the above it's important that enough glue is used so that it can fully wet the joint face on both sides and that sufficient clamp pressure is applied2. You want to clamp hard, firmly enough to squeeze out all excess adhesive because a thin film is nearly always the strongest3
A little more on some aspects of this in What are the different grain directions, and how do they affect joint strength?
1 These surfaces should be waxed or otherwise protected (e.g. with tape, packing tape is excellent for this but just about anything will do) so that any glue that squeezes onto them won't bond them to the workpiece.
2 Many woodworkers, including some pros, under-clamp and the fact that there aren't more joint failures is a testament to the bonding strength of glues. But where joint strength is critical, and in butt joints the glue is the only thing holding the wood together so it's a critical example, you want to tick all the boxes and that includes very strong clamp pressures being applied to ensure a thin glue line. In butt joints we should be aiming for glue lines that are nearly invisible, certainly not easily seen at arm's length.
3 An exception would be when using epoxy, which doesn't require clamp pressure to ensure a good bond and which can make a very strong bond even in a thick film.