Reading glasses, those off-the-shelf from a rack with a positive prescription, are not for those that need prescription glasses. They are for older individuals who still can focus at distance, but who have lost the muscles and lens plasticity to focus their eyes on closer objects.
The eye becomes able to focus on a smaller range of distances in older age, and for a person with good vision who has not needed prescription glasses, this might mean they can focus from infinity to 100 cm instead of infinity to 10 cm of their youth, making reading a book difficult.
The majority of those needing prescription glasses are myopic, or short-sighted, meaning that they can focus well on close objects, but cannot bring far objects into focus with their eye's lens. They will never be able to see far objects such as the stars clearly without optical correction. Unfortunately, after correcting the vision with prescription glasses, the same problem also occurs in older age, individuals can no longer bring closer objects into focus while wearing prescription glasses.
Simply taking the glasses off allows for seeing close objects again, but is suboptimal. First, the prescription glasses likely also correct for astigmatism, another type of distortion in the eye's lens or shape. Secondly, uncorrected vision in people that are quite myopic, such as myself at over -4, means that I can read a book when held a bit closer than would seem normal, but cannot focus on 2x24" monitors when they are 0.5m away, computer monitors are too far away to see. I would travel the world in a bubble where only things 15" or closer can be seen without glasses.
When the eye's lens becomes less plastic in older age, this may mean that the 0.5m monitor can neither be seen cleary with traditional prescription glasses or without correction. A second pair of glasses could be tuned for things 0.5m-5m away
The problem with bifocals and progressive lenses is that they assume you are looking down to see close objects. For those that do close-up work, from SMD soldering repair to dentistry as well as individuals working in front of monitors, they are not a good solution, as the work is directly in front of the eyes.
One practical solution for computer work is 40" 1080p monitors at a farther distance. This takes research when subsituting a television, because many HDTVs that one might try to use at 1920x1080 do not have clear 1 to 1 pixels as advertised, even with digital input.