The biggest benefit of visiting in spring is the awakening of the park after a long winter. In late April, wildflowers are blooming in west Merced River canyon. As the first buds of tufted poppies and spider lupines explode throughout fields, this is the first mark of spring, and there is more beauty and life to come. Waterfalls are also rushing this time of year, as snow melts at higher elevation. And, wildlife is out and about, excited about warmer weather and lush green land.
Another benefit of visiting Yosemite in spring is the lack of the crowds that summer brings. There are definitely more visitors than in the winter months, but it is much more manageable than the summer. Also, while most trails remain snow-covered in April, some trails in Yosemite Valley, Hetch Hetchy and Wawona may be snow-free in April.
Lastly, Mariposa Grove Road typically opens in April. While it is closed, you are still able to car your car at the Masiposa Grove Welcome Center, and take the 2 mile Washburn Trail to the grove. Once the road opens, you can park your car the Welcome Center, and take a shuttle bus to the grove; the bus leaves from the parking area every 15 minutes.