#1 - Last Click model will spread out your conversions across more of your campaigns. Meaning if you a have a search campaign and the converting person clicked on it but later converted via a Display remarketing campaign. Only the display remarketing campaign will get credit.
#2 Time Decay attribution model will according to Google "Gives more credit to clicks that happened closer in time to the conversion." Meaning that the display campaign will get "more" credit since it was the most recent and last campaign to touch the person before converting BUT some attribution is given to campaigns which touched the person earlier on.
Hope this answers your question.
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