A sort of “ultimate spellcaster,” cleric/wizards can draw upon a truly enormous number of different magical effects. The risk is that by splitting their focus this way, they will become a jack of all magical trades, but a master of none.
However, the advantages are also significant. A character focusing on the wizard side of their training gains a boost in hit points, healing magic, weapon proficiencies, and likely some armor ones as well.
On the other side of a the balance, a character primarily focused on their cleric levels gains exciting offensive and utility spell options, the ability to recharge a few spell slots on a short rest, and some useful scholarly knowledge.
An even mix between the two will have a dizzying number of spells prepared at once, but they will all be lower-level options, which means that it’s generally a better idea to focus on one class or the other.
[[Synergy Feats for Multiclassers#Cleric w/ Wizard|Cleric - Wizards chains and ideas]]