Mantras are to be recited with perfect grammar else it may mean something else. The vibrations which are produced by chanting the vedic mantras are very powerful and said to heal many inner & outer diseases. So one has to learn them from masters who know the complete meaning & purpose the the mantra. They have to be learnt from person to person with correct pronunciation.
Temples are the spiritual centers. One learns how to build character through the puranas or the speeches delivered there. One learns the joy of sharing by doing charity or learns from others who does there. Soft skills which are presented to please god like singing (music heals), dancing (reasoning skills), poetry (imaginative & creative skills) will take us to next level both spiritually and also with worldly knowledge. Temples energize us like this in numerous ways which may be difficult to explain all in one answer.
Idols of god are installed with vedic hymns in Garbha gudi, the process is called prana pratista meaning after that process god Himself/Herself lives in that murthi. Everyday god takes different upacharas from suprabatham to unjal seva through that murthi. This creates the divine environment around the temple and one who visits temple gets peace and confidence in account of unrecognized energy set around. So, if such powerful god is taken photo, kept in home, people may become lazy to visit temple often they may convince themselves on seeing the image taken.