What is the difference between 缩减 and 削减？
缩 = shrink; 缩减 = shrink / reduce
削 = cut; 削减 = cut / reduce

缩减預算 you can shrink the a budget to reduce it's size. (budget as a whole shrinks )
削减預算 you can cut the budget to reduce it's size (sum of money or items in the budget being cut away)

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缩减開支 you can shrink expenditures to reduce it's amount (expenditures as a whole shrinks )
削减開支 you can cut the expenditures to reduce it's amount. (sum of money or items in the expenditures be cut away)

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削减僱員 you can cut employees to reduce your company size. (individual employees being cut away)
缩减僱員 you cannot shrink employees  ;  you can only 缩减僱員人數 (shrink the number of employees)