You do not necessarily have to bleed the brakes when changing brake pads if the brake system remains sealed and no air enters the hydraulic system. Simply changing pads usually doesn't require bleeding because you don't open the brake lines, so no air gets in. However, there are some important points to consider:

• If you opened the brake system or brake lines during the process, bleeding is required to remove any air that may have entered.
• Compressing the brake caliper piston can sometimes cause fluid displacement back into the master cylinder. If the fluid level is low, air may enter, so bleeding might be necessary.
• If you notice a spongy or soft brake pedal after changing pads, it's a sign that bleeding is needed to restore proper brake pressure.
• If the brake fluid is old or contaminated, it's a good practice to bleed the brakes when changing pads to ensure fresh fluid and optimal brake performance.

In summary, bleeding brakes when changing pads is not always mandatory, but it is recommended if air enters the system, if the brake fluid is old, or if you experience any braking performance issues afterward. Checking brake pedal firmness and fluid condition will help you decide if bleeding is necessary.