Does keeping the boom extended put extra strain on hydraulic cylinders and hoses?

Yes, having the boom out does add additional stress to hydraulic cylinders and hoses. Here's why:

1. More Pressure on Hydraulic Cylinders

Seal Constant Load: With the boom out, the hydraulic cylinder is in a constant load state, so the seals and packing feel constant pressure. This can result in seal fatigue, leakage, or internal bypassing (leakage of fluid past the piston within the cylinder, causing drift) over time.
Rod Exposure to Damage: The cylinder rod, when extended over a longer duration, is exposed more to water, dust, and possible impact. This subjects the rod to higher corrosion, scratches, or pitting chances, damaging the seals during the retraction of the rod.
Uneven Wear: A cylinder that stays extended for longer periods can have the internal wear of the piston and barrel become uneven, influencing the long-term operation.

2. Additional Stress on Hydraulic Hoses

Constant Pressure Holding Load: When the boom is out, the hydraulic system has to keep pressure to hold it there. This over time can increase hose fatigue and lead to more leaks or bursts.
Increased Hose Bending and Stretching: Hoses on the boom might be at maximum extension, and this can result in premature wear, cracking, or internal delamination—particularly in cold climates where rubber hoses are less flexible.

Thermal Expansion Impacts: Longer booms allow hydraulic fluid to be under pressure for hours at a time, resulting in overheating. Excessive temperatures will break down the fluid more rapidly and wear hoses over time. 

Wear Minimization Best Practices

Retract Wherever Possible: The boom lowering and retracting lessens the hydraulic pressure load on seals, rods, and hoses.

Employ Boom Locks or Supports: Should the boom extend, mechanical lockup or protective props decrease hydraulic pressure dependence.

Routine Inspections: Look for leaks, hose cracks, or damage to the cylinder rod, particularly if the equipment frequently runs with an extended boom.

In general, leaving the boom extended puts extra wear on hydraulic parts and should be avoided when not necessary.