Why would you have a need for an adjustable bedside table? For one thing, they are great if you eat in bed. Also good if you read, write or do crosswords in bed. The foot of this type of table slides under your bed frame, allowing the top to be right in front of you, rather than next to you, as it would be with traditional bedside tables. This means a stable surface right where you need it.
Here’s an example – not much to look at, but does the job, I guess:
Adjustable bedside table pictured: Think Tank Technology KC68151 KCO Group Adjustable Swivel Laptop Desk
When it comes to these types of tables, the quality varies greatly.