Since the pros and cons for the US have already been addressed, I take this opportunity to address the pros and cons for Philippines with regards to the annexation.
There are numerous benefits the Philippines would have enjoyed due to the US intervention, among the notable benefits include:
The freedom from the Spanish: The US was opposed to the Spanish form of governance. The Spanish were brutal and this forced the US to intervene. The victory by the US over Spain at Manila bay ensured freedom for the Philippines.
Protection from other empires similar to Spain: After Spain was defeated other nations such as Japan and Germany were interested in annexing Philippines. The style of governance by these countries would have taken Philippines back to where it was with Spain. Apart from protection, the Philippines would also benefit from military training and equipment to improve their defense.
Employment opportunities: Philippines would benefit from the establishment of a trade hub by the US. This trade hub would have provided numerous employment opportunities and economic development.
There are negative implications of US annexation of Philippines and these include:
Loss of sovereignty: The Philippines wanted to earn their independence in order to plan and make decisions for their future without external interference. Achievement of this objective would be hindered due to the annexation.
Culture interference and distortion: Some of the cultures and traditions of the Philippines were opposed by the US. This eventually would lead to the loss of cultural memory in Philippines.