I'm restoring an old tube radio. When looking into the schematics I noticed that they drew 2 resistors in parallel instead of 1 resistor, between the power transformer and the rectifier tube. Is there any benefit from installing 2 parallel resistors instead one resistor?
Two resistors have an increased ability to dissipate power/heat, up to twice the time one can, when mounted with enough space between them.
Also for a few applications it is easier to find two standard value resistors that together form one resistor value that is not among the standards you already have in your BOM (or are available).
Lastly for the gray beard hand chosen value resistor, it might have a higher yield to use two that are slightly off than to find the one that matches perfectly.
The benefit is the power dissipation.
If you have a voltage V and a current I the power dissipation across a resistor is
$$ P=V \cdot I$$
Now if you put two resistors in parallel you divide the current in each resistor by 2 (if they have the same value) and then the power dissipated by 2.
Sometimes it is cheaper to put 2 resistors in parallel to dissipate more power than only one bigger resistor.
As others pointed out, the main reason increased is heat dissipation. I had a sound amplifier that had a huge power resistor which every week was burning out literally. One day I replaced it with 2 resistors and since then never failed.
Another experience of mine is regarding PCB design. I wanted to order minimum variety of components. So the pick and place machine won't charge me for extra rails. I had many 5k resistors in the design. Anywhere that I had 10k or 20k resistors I simply used 5k in series. A bit stupid but saved me few cents!